Power machineries, such as hydraulic excavators, cranes, wheel loaders, and bulldozers, (in the present description and claims, these power machineries (heavy machineries) are collectively called “operating machines”) have been used for civil engineering works, construction works, and the like. Taking the hydraulic excavator as an example, the hydraulic excavator is configured such that: a revolving super structure (structure) is provided on the upper portion of a base carrier; and the revolving super structure includes an engine, a driver's seat, an arm having a tip end on which a bucket is provided, a boom coupled to the arm, and the like and is thus a large heavy structure. By manipulating a remote control valve at the driver's seat during operations, the revolving super structure is caused to revolve on the upper portion of the base carrier, and various operations are performed by the bucket provided at a tip end of the arm. The revolving super structure is caused to revolve by a driving device configured to cause the revolving super structure to revolve. In recent years, a device including a hydraulic motor and an electric motor has been proposed as the driving device.
One example of the operating machine including this type of driving device is an operating machine described in PTL 1. The operating machine of PTL 1 includes a driving device having a hydraulic unit and an electric unit. The hydraulic unit includes a hydraulic motor as a driving source, and the electric unit includes an electric motor as a driving source. The driving device is configured to control the electric motor by a controller and an inverter at the time of revolution and assist the hydraulic unit by the torque of the electric motor.
According to this operating machine, when the driving device performs steady revolution or decelerates, the electric motor is caused to perform a regenerative action, and regenerative electric power is stored in a capacitor. Moreover, at the time of the revolution, if a revolution speed or a revolution acceleration rate is equal to or higher than a set value, and the amount of electric power stored in the capacitor is equal to or smaller than a set value, a control unit of the driving device causes the electric motor to generate the regenerative electric power and stores the regenerative electric power in the capacitor. According to this operating machine, the control unit calculates the torque required at the time of the revolution. When the obtained required torque exceeds a set value, the electric motor is caused to output necessary torque.
The control unit controls output torque of the electric motor while shortening as much as possible a time in which a relief valve provided at a hydraulic motor circuit discharges oil. With this, energy loss by the relief valve is suppressed. Further, by providing a buffer poppet on a spring side of the relief valve, a boost buffer (shockless) function is performed at the time of acceleration, and the relief operation is performed after the oil pressure reaches the peak.
As above, according to the operating machine, the maximum torque can be secured as a whole by assisting the hydraulic unit by the electric unit. Moreover, the necessary torque can be generated by adjusting the torque generated by the assist of the electric unit. With this, the energy saving and the prevention of the generation of hunting caused by excessive torque can be achieved.
As other prior arts, there are, for example, a construction machinery described in PTL 2 and a hybrid construction machinery described in PTL 3. The construction machinery described in PTL 2 includes a hybrid driving device having a driving force synthesis mechanism configured to synthesize the driving force of a hydraulic actuator and the driving force of a motor generator. In addition, to effectively utilize energy generated at the time of braking, the construction machinery is provided with a communication valve (bypass valve). With this, inertial energy of the revolving super structure is tried to be efficiently regenerated as electric energy by the motor generator. The hybrid construction machinery of PTL 3 is configured such that: a pressure difference between both ports of the hydraulic actuator is detected; and a torque command is output to the motor generator, provided close to the hydraulic actuator, in accordance with the pressure difference.